The present invention generally relates to copying apparatuses and more particularly, to a copying apparatus in which cleaning of a photosensitive member, i.e., an operation for removing residual toner from the surface of the photosensitive member is performed at a developing device.
Generally, in copying apparatuses, after a photosensitive member such as a photosensitive belt, etc. has been subjected to exposure and development such that a toner image on the photosensitive member is transferred onto a copy paper, a small amount of toner remains on the surface of the photosensitive member. In order to remove the residual toner from the surface of the photosensitive member, a cleaning electrostatic brush is applied to the surface of the photosensitive member after a residual electric charge has been eliminated from the surface of the photosensitive member by using a charge eraser, an eraser lamp, etc. Such a method has been widely employed in which an electrostatic brush for developing a latent image into the toner image through application of toner to the surface of the photosensitive member at a developing device functions also as the cleaning electrostatic brush in order to make the copying apparatuses compact in size and light in weight. This known method requires two rotations of the photosensitive member, i.e., one rotation for a developing process and the other for a cleaning process and therefore, is generally referred to as a "two-rotation process". However, when a high resistivity carrier such as a resin coat carrier, etc. is employed in place of a conventional iron powder carrier, the cleaning process does not work sufficiently. Thus, in order to meet a recent demand for copying of high image quality, there has been proposed a "three-rotation process" utilizing three rotations of the photosensitive member, i.e., one rotation for the developing process and the remaining two rotations for the cleaning process so as to perform the cleaning process twice such that residual toner is sufficiently removed from the surface of the photosensitive member. The prior art three-rotation process is advantageous in that residual toner is sufficiently removed from the surface of the photosensitive member. However, the known three-rotation process has such a drawback that since the photosensitive member is required to be rotated three times during one copying operation, the copying speed is undesirably low. Furthermore, the known three-rotation process has a disadvantage that when an original document has an image of a light shade, the first cleaning process suffices for removing residual toner from the surface of the photosensitive member, thereby making the second cleaning process useless.